The architecture of complex computers, business machines, communication systems has largely developed around the use of a backplane, or mother board, which interconnects multiple daughter boards or cards carrying functioning components designed to define a host of memory and logic functions and the necessary electrical components to effect a signal generation and transmission. Various circuit paths on backpanel and daughter card are interconnected, typically through connectors which engage such circuit paths mechanically with a normal force between contact surfaces sufficient to establish a stable, low-resistance electrical path. Increasing circuit complexity has led to an increase in contact density to a point where hundreds of circuit paths must be interconnected between a given daughter card and a backplane, there being numerous daughter cards associated with a given backplane. This, in turn, has created mechanical problems in that the cumulative normal forces required to effect such an interconnection sometimes exceed 50 or 80 lbs. per card, per side of the card, and all are on extremely close centers, frequently in multiple rows on a given side of a card to require extremely accurate dimensions of the boards, connectors, contacts and the like. A still further problem has to do with the surface finishes of the contacts of connectors which may be contaminated in inventory or in handling and cause a variability in resistance between paths which, in the presence of high speed signal pulses transmitted therethrough alter to the resistance and impedance of the circuit paths to a detriment of circuit function.
U.S. Pat. No. 4,969,824 is drawn to a high density connector which utilizes a type of spring known as a canted coil spring made coextensive with the arrays of contacts to be interconnected between backpanel and daughter cards as the main force driving element. A further development extends the use of the canted coil spring to include a spring made of shape memory alloy and provides a rigid tubular bar structure adapted to hold such springs in engagement to effect the interconnection of contacts. This Application also includes a flexible film strip wrapped around the tubular rigid bar so as to hold the contacts in place and provide an even pressure from the springs against such contacts.
U.S. Pat. No. 5,092,781 adds features allowing for an operation of canted coil springs made of shape memory alloy to provide a displacement allowing for either a low-insertion withdrawal force or a zero insertion force, with respect to daughter card and backpanels. U.S. Pat. No. 5,098,309 similarly employs rigid bars, thin flexible films carrying contacts in circuits, and additionally provides a mechanism wiping and backwiping the contacts through a particular cam motor structure.
In each of these cases, the rigid bar structures are applied to the backplane with the daughter card fitted between such structures, and the structures operated through mechanisms to effect a clamping together to provide an interconnection between the circuit paths of the backplane and various daughter cards. Work with these types of interconnection systems has uncovered a number of problems, including the need to provide extremely closely dimensioned board surfaces, including the contacts thereon interconnecting the board circuit paths in order to assure an adequate mating of the large numbers of closely spaced contacts required. Problems with the straightness of boards, particularly daughter card boards, and with damage to such boards caused by the relatively high forces involved, have been uncovered.
Accordingly, it is an object of the present invention to provide a high density interconnection connector which assures a proper dimension of the area of interconnection between circuit boards. It is still a further object to provide a connector which is applied to daughter cards to strain relief and straighten such cards to assure dimensional compatibility relative to interconnection with a backpanel board. It is yet a further object of the invention to provide a connector for providing an interconnection between contacts on boards which are on close centers in multiple rows extending over an area of the boards and including wipe of the contacts.